Day 21

4 files changed, 1746 insertions, 0 deletions

diff --git a/day21/input b/day21/input
new file mode 100644
index 0000000..c441f08
--- /dev/null
+++ b/day21/input
@@ -0,0 +1,1619 @@
+cgrb: gzwb * rcfd
+gfbz: bwgp - qlfm
+jrbf: 2
+gvvg: rjch + tjdp
+vwsh: grwp * ddsv
+tpwb: 1
+vjtv: 3
+msjg: tdml * mrgt
+snmc: gqls * hcpg
+vhps: dmmr * ggfh
+mmtm: vmvg + nrvn
+ppgv: jjcs + wwbd
+bpfp: 2
+qbqs: pqsn * gqmd
+dtqj: hwqn + vmlg
+ppfj: 2
+wncv: dpzh / jghw
+bsfb: 11
+jftc: 2
+cndz: 3
+pnvj: tnfn + tpmn
+sbqn: lhcd + tbqv
+dprz: 2
+ztlv: vvvw + vlmw
+grvf: 13
+pjcd: 2
+tfdp: 5
+dmmr: 4
+twts: 7
+trbj: nzrj * jcjm
+fsnr: 3
+ttws: whhz * ljnv
+jjqd: nvhn + bsfb
+smcn: 3
+jcjm: 7
+zqjm: 2
+cggq: snzc + glmg
+wqlv: 5
+gzbv: vjjv + fmzz
+mvwl: hbbt * mbcs
+rhrv: chhr * rqfs
+bjfp: 15
+fzhh: 2
+clrz: 3
+tjrw: wshw * qvwn
+tjlt: 4
+dmfn: ngtj / bwtf
+fplt: nvdw * qnvj
+stms: 3
+sslh: hgqw * tgcb
+wdwn: ltnn * cfbh
+nbgv: npwd * pqrt
+hpzs: cdsp - jvpm
+mcjt: ngqt * qdcf
+pdpn: 12
+hnpp: 9
+ffwm: 6
+hhpg: 3
+zwcl: mbpm + nrmd
+zqbv: 2
+trqr: 3
+brlr: 2
+nswj: 1
+hfpt: mhpj + mdbm
+bjqq: 4
+jhhz: 2
+qmmf: 15
+nwds: 5
+nmqc: 1
+npmb: tbfw * hzjl
+qzjj: 7
+vnzw: 13
+hdrw: zngj + sqdg
+pgpb: 14
+ztgb: 2
+lrjl: jcrv + fdll
+gqsl: pmpp * cnwr
+vbtw: 3
+wpzj: 2
+hvjb: qrqb / brlr
+spwc: 2
+htmn: 15
+zmmr: 2
+tspd: jlvw * nprf
+zwgf: fdzw * ffdp
+gtmh: 5
+qzcv: 2
+tqwm: lhnq + lffd
+ntrm: ftlv + pnrw
+hqjb: 2
+hbww: ztlv * dwnc
+jdms: rbjm * zvzf
+zlrn: fmjm + zlwr
+rhnp: vrmz + vnzw
+bncr: 10
+nnzh: wcgl / cvtz
+bqqz: 5
+czpn: qpgr + hflr
+hdlj: ljfj * fmgb
+cqlb: 17
+wpzr: mfwq / rdlj
+snzc: qgfd + nmls
+zdcf: ctlp * nptz
+djbr: dbcf - msjg
+zjcc: nrhh * ddqb
+rdgh: 9
+lhjl: lvml * qbps
+flfj: 2
+nwwq: 2
+hsqn: 3
+hvlz: gdrq * mqvd
+gfzg: 2
+qrpm: 4
+ljfj: 11
+hdzg: 3
+qgln: 12
+wmld: 9
+vsnq: mlrh * cbwl
+mqvd: 13
+cwft: 2
+nssp: 8
+wpzw: clzz * vdhn
+rlrt: 6
+pslc: hrdw * dvjb
+lffd: bnff * svsm
+rzct: 1
+qhdj: 10
+bdwg: cctg * zvjt
+nflt: ggpq + csln
+fjdr: tdgm + gnjn
+wqnv: bfms / lrnn
+hzjl: 5
+vszz: 18
+mjhj: 3
+trts: przz + hrqz
+ljdc: 3
+jghw: 2
+hmqf: 2
+fjvr: 2
+qtch: ltft / nflj
+ffvf: 1
+pdbh: 13
+jncj: cbzf + tshw
+grwp: tjlt + pgpb
+tsnw: humn + sslh
+llnz: dphw * lqjs
+bbhd: 2
+rmwv: tzwl * qthg
+mlvm: 3
+bpmg: jqnq + qjgz
+pjpz: 4
+hbbt: 2
+wmtp: 16
+spnw: 6
+rwtw: rlqz / rrjn
+bhtl: 8
+vbmj: jbtq / hqjb
+tjfs: 2
+dwjs: rbbm * fmjq
+strh: grcb * smsd
+pnnc: cfjf + rhrv
+mfsv: hqfh + tmhz
+ldwr: 13
+nrvn: vbnf + lljr
+rsgn: 2
+fmzz: tzdw * vcbr
+tdml: 3
+wgvd: tgmh + lnvp
+zjjd: 5
+nlcm: lfpm / hfng
+vpmh: tnfw * twts
+ljfq: 2
+swzm: 4
+rcfd: 3
+wmhm: jrhj + qfld
+zdmw: wrbz + bdwh
+rczv: ggtj * ttff
+djhn: 17
+nghf: 4
+nqbv: 3
+dpmj: tjmj + rcpv
+rdlj: 3
+tdgm: djbr * zqbv
+rshb: jncj + npws
+jpsh: 10
+shvt: 2
+mrgt: wbfn * wszg
+mjbr: rmhc / wchb
+jbln: jnsw * zdtc
+hmtl: 3
+qdcf: 9
+pthw: 2
+fmgb: 2
+sqhn: fcjw + qtfw
+rwpc: jrhz * fjcm
+mrzf: 2
+rfnz: 3
+tzdw: 2
+dwrj: tjfs * msns
+phlg: jlss + jrfr
+wtvd: ctqt * cctn
+gjjl: lprh + gzlf
+zdlw: zfgn + pprr
+fnll: tqvg + ddlb
+ftpz: 2
+vcbr: lclb + tqlj
+nhzg: 13
+hwvl: dmpf + gwhd
+fhvq: mngn / zjqh
+mhdh: 2
+cmbl: 15
+dhzt: 9
+zbdm: dqcc + slld
+trfn: nfpd * bgqg
+pvqr: fvln + bjll
+smlg: 3
+pbpf: 11
+gzjr: 2
+tqmm: 3
+phnj: 12
+phfv: blpp + mbgm
+dzbz: 5
+tlsj: 5
+vbnf: 3
+vfbc: 3
+cvzg: 4
+rpqt: 5
+wnsr: 3
+pmwt: 14
+dlbr: hhjv + jpcr
+cbbh: rfzd * gwrh
+stdj: 3
+jzzp: 3
+wjfz: 11
+jjrc: htjj + wqdn
+ccgr: 2
+sppm: thtt * nvbb
+blvh: jcjf + zbmp
+wtzp: 2
+swlb: rjzp + qffj
+dszm: 4
+rndr: qbnh * hcsl
+lbts: bdng + brwc
+tvzv: rwtw + brvj
+rjzp: plbn / rwhw
+vdhn: fnll * qnnr
+fpch: 19
+wwzl: 2
+wgnc: 2
+lmfz: 9
+cndr: glpw + hlsm
+lnvp: 5
+gvzt: 6
+shjg: 5
+tjht: 1
+zsbn: lsnh + dptl
+ltrw: btvs - nzqv
+tlqh: bzpt * qmmf
+jvpm: 2
+cvpt: 2
+gfmz: 6
+phrq: vnwg * qsjw
+ndzf: hnpp + rvfg
+snvw: 2
+lnrq: nbtl + vszz
+tmhz: 6
+lcsc: 2
+tmhs: 5
+glsg: 3
+jzff: zdlc * hjpt
+chvw: 4
+pzsv: 7
+sqcg: 2
+wnml: 11
+bjjn: cbtg * lczq
+lzfw: jmbp - nwwd
+fvvn: 10
+vrmz: 18
+qfhp: 4
+szjb: wwwv + vrpc
+htch: 2
+dvps: 4
+qctd: 5
+rcmp: bqwt * dczs
+fpgn: dtpm + vlgl
+vbvm: mtjt + tthm
+gzgg: 5
+hvgb: 6
+mdbm: 12
+dfnd: 3
+qmvh: 14
+bwtf: 2
+bllg: 7
+nzhv: 2
+mlwh: 14
+vgbr: 3
+svsm: rvdr + hdwp
+nvhq: hsrh + qnpj
+sjqq: 3
+gtwc: cvfg - lnrq
+twww: zrmh * zsgf
+gjqf: 4
+mhrs: bmlr * sqjd
+vrpc: 7
+swsb: tlsj + szww
+lhcd: mnwb / pdcp
+hgqq: zqvv * bnfw
+frdf: 2
+dmnv: pmgh * bqpl
+qvqt: 16
+jpvw: scvl + nvtd
+tjdp: 2
+fmgj: ndzf / spsh
+qhgp: gvvg + rgwv
+fqbt: gzsr - zwcl
+dztv: 4
+dqlh: 1
+ljbr: 5
+cvtz: 2
+dnwq: pvts + pwhd
+fbgg: zwjl * nfvl
+zzgb: 3
+pwpw: pprn + llzn
+wwwv: gbgl + vtfn
+jjrh: 8
+qnvj: qtcc + ptld
+fqsl: 3
+gdbc: 2
+fstq: ngcc * qqzf
+bdth: rzct + hbqr
+hptn: vtdr + mcgv
+ntll: wqmf * swzt
+fzmq: dlzs + sqsp
+bnpt: bpsl * pllf
+mlbz: ncrn * mmnh
+mlns: 2
+ctcs: ttzd * pbqv
+tvhr: fdfl * sdjs
+mzrp: gndt + pnnc
+ngcc: 2
+jtfj: mvwl - zrdf
+ttff: zwcv + dwjs
+prjz: zrfh + jrjs
+nvcq: hngp * qhdj
+tfwt: gdwm * bjfp
+ssnf: 5
+bpbz: 3
+bghs: 3
+dmmw: 1
+tmtl: bpfp * nflt
+gmjw: dsrv + dstb
+jdnd: tvld + wmtp
+rpjn: 3
+qcdq: fzhh * hmtl
+jcjf: 11
+sqqh: 3
+wdtq: qvqt + tztb
+shhg: 10
+vclb: dclb * mtlb
+swqj: 2
+mlwj: vglm + trbj
+lfpq: gstj + dhzn
+dqcc: 14
+spsc: 8
+rtbm: 2
+gntr: cnvs * jnht
+tnfw: 2
+gstj: cmgs * mhth
+pqsl: 8
+vlvr: nnzh + cwcj
+bnhw: cvrr * hsjc
+wtsf: 2
+lnzc: lqft * qmvh
+mmfp: wtsf * qjdb
+qcvv: 2
+cmvj: jtpg / njcm
+rlbv: 2
+gcwr: gqsl + tnnv
+wjpz: 6
+gjvt: 2
+tnnv: ffbw - hpsb
+hgqw: cdvb + rqnr
+ptdp: 4
+lrth: 17
+jdrl: 5
+tvct: sjbd + vsnq
+jndd: 3
+dcfd: 13
+cbdl: cqcr * cttg
+zbbm: 16
+mwdh: nbzm + jgdd
+gstb: 2
+gblj: 7
+hjpt: 7
+njnw: tpwb + sdvs
+vmvg: 4
+qpgr: bcmd * cjmh
+jrfr: 2
+nzhb: 2
+qlnv: 2
+wqdn: 3
+jfjt: 7
+cbtg: mfhj - czsg
+fmqb: gmgr * nhnp
+lwnc: 17
+wlzq: 5
+wwbd: 12
+gqmd: 3
+lwzs: 5
+vtfn: 3
+sbft: 9
+hhjv: 13
+vlgl: mrsd + sppm
+hfbp: rcrf - hnpn
+wbcr: gflt + nsqg
+lbdp: 1
+hgdh: zbbm * qnhb
+prnm: dhft * swqj
+gwrh: 11
+pfbp: 17
+ltnn: 2
+jrjs: wgqw * whbw
+ngqt: 16
+qzrh: fmqb + cbbh
+vnqn: fjvr * vmqc
+gftz: ghvf * rfwz
+hznt: qjwg + qnph
+dtsq: bjbc * rpcr
+jrhz: 3
+mqql: 3
+jnht: 5
+wwhw: 15
+fwgz: 3
+nhdb: pjzc * fnml
+bdwh: 6
+mnwb: bnpt / qjpl
+rqjq: smcn * bzst
+vlmw: 8
+ddlb: twrl + sdfs
+tzqq: 2
+plbn: tbpv * hcsd
+vnqf: rzcf * pthw
+tqbr: blfj * dmfn
+nhnp: lcvp + qfms
+bjfl: 8
+flrv: 13
+zstd: 2
+swhl: 2
+hcsd: 3
+rzcf: pvqr + cbwv
+pssd: twww + ctcs
+qmpz: 12
+mwhj: dwph + szjb
+dptl: zrwg * mwdh
+bjbc: 2
+dwrt: 2
+wnpc: lhbs + tpgw
+trws: lzwt + hmlp
+gzwb: lpml * zhqg
+mjsh: 6
+cnnp: 5
+wlng: jbwt * bpmg
+hhmt: gfbz + hvrm
+qffj: jqhf - pmbc
+cbqp: lnwj * hscl
+mdwb: tcff + ttws
+nrrc: znsn + mcsm
+htjj: 5
+tbfw: 3
+gzsr: tvct / vstc
+fnfl: 2
+mbgm: 15
+tccl: nqcp + wbcr
+wnsv: 3
+rfbj: cmbl * phfb
+phfb: vtzw * lqbd
+dmtn: 5
+brwc: ptbz * dttp
+zbdl: fhvq * wvgf
+ngtj: hwlt * cfdz
+dvvq: vfrn * cqpm
+rfsn: 4
+bqdd: zstd * fnqt
+jrvv: ndhj * vslr
+dlzs: jwrl / vbrr
+jjhd: 6
+lmwn: vbdt + vsrl
+jbfv: 2
+jcrv: fjdr / nwph
+fhwg: hbww + blsv
+jppc: tgnj + lcjd
+jtwn: 9
+jpqm: fbwz + dljv
+cctn: bgws + dmrh
+lcbh: cfpv * bqdd
+jbrc: 2
+gczs: 5
+hdmb: gtwc * qcvv
+ptsj: 2
+rvdr: hvhh + nmqc
+znsn: 4
+gndt: 1
+qncn: frdf + ltdp
+pmbc: vzft * pvrr
+dntg: hdmb / chqf
+jshb: 8
+qfms: cdmm * tnlr
+rvps: 7
+fplf: 2
+plhr: mfsh + prnm
+lqlz: 2
+qnts: vlqq * sgsz
+wwpm: qjdf + lbmd
+tvvl: 1
+phrc: grpr + shjg
+cjrq: 8
+nbmm: 5
+ctqt: ptsj * cwjz
+jbtq: wnpc * swhl
+mfpg: njnw + ntll
+fnfn: sjsf + fdbm
+sbtw: qtch + tztc
+vzwh: wgvd * mpsg
+qsgs: qgln + zdmw
+vlqz: shzv + dnjl
+qnhb: 16
+qtjp: cfqw + dhjv
+mwpw: 7
+vnwg: 2
+rcvc: 1
+gnmm: 2
+ltlg: 2
+tqvg: nfqw * zzqz
+rcrf: tlfr / bllg
+ggtj: rqpw * rdgh
+pdbs: pcwg * lgbs
+pgpz: 3
+tvld: 10
+ptth: cbqw + qwdf
+mhsn: 2
+qnph: htfd * pjcd
+hpvv: sbtw + qdcn
+sqdg: fdfq + tfww
+bbnr: rznq * fhwl
+rvqg: 4
+rfwz: 4
+mvsj: 5
+jmrh: 11
+mdjn: mtgh * wpzj
+vlfr: 5
+ddqb: wmhm + vjzf
+mszq: 3
+whqj: ltpz + ttnz
+cqpm: 2
+rlvh: 2
+ptcp: qbvw * fwjf
+jnbz: 3
+fprr: 5
+wchb: 3
+qqqw: nntf * hhpg
+hnzj: 3
+ggfh: 7
+tqvh: lbts * mlvm
+hdwp: mhsn * tgjv
+qnnr: 2
+ptld: cnmf * ghss
+gpmm: 2
+njvf: qdvl * cjzn
+gdwm: 2
+pbdb: qcrp + sdsh
+sjsf: 7
+zqrp: nbgv + wsnr
+dtpz: scll * sfww
+zrmc: tpvw / sqqr
+dhft: jdgp - rtqz
+bfms: wjlr / lpvw
+dlfm: 2
+chhr: 3
+vlcs: wlzq + frvp
+pvdl: dnrw * ltlg
+dvll: 2
+hhrv: 2
+tndw: shqf * qfjq
+sdsh: ptcp + mdjn
+hzmj: tcfr - clqd
+rqcq: 3
+gqfs: hnnz * fcpv
+mmhg: 4
+vszv: 2
+hnqd: 15
+mjwn: mdlq + pssd
+fdpm: 15
+fpzz: zqjm * vgfw
+zrfh: 1
+ppts: 2
+rmhc: ltvr - snwl
+jttq: gwzh - wtvd
+cpvl: wtrv + ldwq
+bzst: mbst + jbln
+qdjl: 5
+qtzz: crbp * lqcj
+dwdc: 20
+cgnp: nswh * dzdp
+mngn: rgpb * qhsv
+gzlf: vssh * prgh
+jtpg: whwf * dtpz
+pmgh: 2
+pscc: jtwn * ztgb
+brcg: dmcf * jtfn
+gdrq: 3
+dggp: 4
+qsjw: 5
+nvdw: 2
+pdgh: 4
+nrqf: pqsl + dnqt
+qjdp: jrfz * hbbh
+gcdz: qtjp * gjqf
+lhhh: hhmt + nvcq
+phhf: lqzz * szzt
+qjdb: bnvr * nhqr
+cgwn: wqzs * mzjz
+lrnn: vgbr * gmwv
+fcps: mmtm * gfzg
+nwmq: mqsm + hvgb
+ctlp: 2
+mbst: mmbb / jbfv
+dzhg: dpmj + njvf
+pwnp: 2
+ttnz: nmnv * rctb
+ffdp: dsjp * ngbp
+tqlj: qfhp + rmwv
+rvvq: qbpj + pjgn
+jhjp: wqlv + jhmt
+rmhg: 3
+clrl: nwds + dtsq
+lgfj: vccd / fjls
+hpsb: 15
+cjmh: 2
+swml: htgf + gzgg
+mdlq: psbd - svpl
+mpsg: 4
+fnbf: 2
+spwv: pjgv * dvll
+slrp: tjsp * fgvw
+sqjd: lrll + mmgr
+djws: zscl / lpbw
+shzv: tlzj + ncvz
+llwj: 2
+gmdw: 3
+vqtr: tsnw / fvbf
+ncvz: 3
+bdng: 3
+ftdw: ldwr * zjpn
+wvgf: 2
+cdsp: grvf * rqcq
+pgtc: 8
+nbzm: 3
+mjzr: nmmd / bzlm
+tlzj: 4
+gbgh: hvjb + cmjf
+wqzs: 2
+bhbt: nqrl * qvnq
+qjgz: rznp / wdqs
+jdls: gtmh + dggp
+hbbh: 5
+gmdt: tspd - vllv
+hbmq: 2
+tlfr: blgm + zqrp
+qcrp: 8
+rfmm: vgfs - dpzm
+mcgv: scbz * mlfv
+vzft: 3
+dzzl: wdtq * nqch
+zlcb: bgww * crgr
+pdcp: 5
+bgww: 2
+rqnr: rcvc + rnfl
+nfpq: 2
+bcmd: cbqp + vslw
+mtbf: 2
+ljjz: pslc - mwhj
+fpcm: fqsl * nwmq
+sgss: 2
+tthm: jvqc - mjhj
+hrfs: dhdm + thlr
+pwls: 3
+humn: 4053
+rjch: 5
+jwpv: jpvw * wnsv
+jtpm: 2
+pvzc: dzqs + phgf
+cbzf: hvnc + tjrw
+wbfn: 2
+dclb: 2
+prqh: 3
+bsds: bvpp * lmtc
+gjsq: ldvq / nbjz
+thtt: 11
+smsd: 4
+fscw: smqh * hqnc
+dpzh: hwvm + vqcv
+spsh: 2
+zdjf: 4
+dqzg: hvlz * pjpz
+lbwp: dwvq + phmc
+nmsp: pbdb - tjht
+lsmb: 5
+tvcv: 5
+dcgn: cdng * wjpz
+wqns: dcgn - btsn
+dhjv: 3
+sznw: dvvg + dwdc
+zwcv: cbdl + fstq
+jbgd: 3
+pvbf: 12
+smnr: dwnz * dhth
+nfrg: tlbr + zsbn
+swdb: rqpf * tqmj
+vtdr: dcfc * tqms
+hrdw: 2
+fqzj: 1
+mqsm: dvvq + sgmq
+mgtl: 1
+dmcf: 5
+zvzf: 5
+scrw: pzsv * gzrq
+mswb: vllh + qtzz
+rfln: 2
+zvpn: 2
+mqzq: 2
+cwqf: sqqh * ttsg
+nnpv: tqbr / rmhg
+zscl: lgfj * bjfl
+bnff: qcdq * dwrt
+dljv: trws + tqth
+gzrq: fqzj + gdgm
+qfjg: 17
+tfvv: 12
+fmjq: bbnr + qdhz
+rrrt: 2
+gnbw: 16
+mrln: 16
+htts: dpfh * nrqf
+mmtz: 2
+mznv: sznw * fzfv
+tthr: 3
+tmqp: 19
+qvwn: 3
+fbwz: hjsb / tjdj
+zfgn: 11
+qtcc: 1
+tgcb: sbqn + mpwl
+qbtc: 17
+nhcm: 2
+zpfg: 1
+gscw: wnsr * rvps
+qbpj: lbdp + tqvh
+fdll: dprz * ddln
+vhbm: rrrr + bbbt
+lljr: rpqt * ftcb
+jpnv: 2
+hfht: 3
+wfdh: dlfm + mrbf
+qvlf: 2
+scpp: 14
+dwcz: 3
+ntjd: 1
+frvp: zsqz * scds
+dtnb: 3
+fgjm: 3
+tbgb: nhcm * bdwg
+srwr: clpr + sfhd
+zwjl: 5
+qcng: 18
+ddln: zbdm + qnts
+hflr: rhtt * wfdh
+rhsr: pmjb * mwpw
+cmjf: tqhw * pvbf
+dphw: 5
+mtlb: flwd - tmwh
+nmmd: rsgn * nmmv
+cvfg: nhlg / hbmq
+lvgq: zjjd * wnml
+vssh: 7
+szpq: 2
+hfln: 3
+pmjb: 3
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+qvtb: 5
+bfnw: 5
+phmc: ldss * gscw
+hhmh: cvzg * mswb
+zrmh: 9
+pwdp: 5
+czsg: bdzv * jndd
+wdqs: 9
+lpbw: 8
+jmbp: pdgh * hdzg
+lvzd: 2
+lqft: 2
+frhz: 2
+vsrl: 4
+wcbz: 3
+mzjz: jqwf + cvmz
+rtlt: qmpz * mlns
+lzwt: zjrr * zbfm
+crbp: 8
+nzqv: fwrr / gzjr
+zdlc: gphg * cjrq
+nwph: mhhd - sjqq
+szww: 14
+nflj: 4
+dqqt: 7
+jlvw: bbph + hwvl
+ltvg: jdls + tvvl
+cppw: zlrn + ntjd
+tjsp: lhhh + dwmf
+sprj: nzhb * msrb
+nqch: 5
+csln: vdzr * rqtw
+cmgs: 3
+tztz: 19
+cnmf: 5
+bqpl: chts / qzcv
+pcwg: fpdf + trfn
diff --git a/day21/part1.rb b/day21/part1.rb
new file mode 100644
index 0000000..4895237
--- /dev/null
+++ b/day21/part1.rb
@@ -0,0 +1,34 @@
+monkeys = $stdin.readlines
+
+nums = {}
+
+monkeys.count.times do |mix|
+  if monkeys[mix] =~ /(\d+)/
+    val = $1.to_i
+    nums[monkeys[mix][0...4]] = $1.to_i
+    monkeys[mix] = nil
+  end
+end
+monkeys.compact!
+
+while nums["root"].nil?
+  monkeys.count.times do |mix|
+    f, a, b = monkeys[mix].scan(/[a-z]{4}/)
+    unless nums[a].nil? || nums[b].nil?
+      case monkeys[mix][11]
+      when ?+
+        nums[f] = nums[a] + nums [b]
+      when ?-
+        nums[f] = nums[a] - nums [b]
+      when ?*
+        nums[f] = nums[a] * nums [b]
+      when ?/
+        nums[f] = nums[a] / nums [b]
+      end
+      monkeys[mix] = nil
+    end
+  end
+  monkeys.compact!
+end
+
+puts nums["root"]
diff --git a/day21/part2.rb b/day21/part2.rb
new file mode 100644
index 0000000..ab88699
--- /dev/null
+++ b/day21/part2.rb
@@ -0,0 +1,78 @@
+def mutate(eqn, tgt)
+  if eqn[6..9] == tgt
+    op = case eqn[11]
+    when ?+; ?-
+    when ?-; ?+
+    when ?*; ?/
+    when ?/; ?*
+    end
+    "#{eqn[6..9]}: #{eqn[0..3]} #{op} #{eqn[13..16]}"
+  else
+    case eqn[11]
+    when ?+
+      "#{eqn[13..16]}: #{eqn[0..3]} - #{eqn[6..9]}"
+    when ?-
+      "#{eqn[13..16]}: #{eqn[6..9]} - #{eqn[0..3]}"
+    when ?*
+      "#{eqn[13..16]}: #{eqn[0..3]} / #{eqn[6..9]}"
+    when ?/
+      "#{eqn[13..16]}: #{eqn[6..9]} / #{eqn[0..3]}"
+    end
+  end
+end
+
+monkeys = $stdin.readlines.reject { |l| l[0...4] == "humn" }
+
+prev = nil
+need = "humn"
+loop do
+  cand = monkeys.
+          select { |m| m.include?(need) }.
+          reject { |m| m[0...4] == prev }[0]
+  cix = monkeys.find_index(cand)
+  break if cand[0...4] == "root"
+  monkeys[cix] = mutate(cand, need)
+  prev = need
+  need = cand[0...4]
+end
+
+root = monkeys.select { |m| m[0...4] == "root" }[0]
+candname = (root[6..9] == need ? root[13..16] : root[6..9])
+monkeys.delete(root)
+
+cand = monkeys.select { |m| m[0...4] == candname }[0]
+cix = monkeys.index(cand)
+monkeys[cix] = "#{need}#{cand[4..16]}"
+
+nums = {}
+
+monkeys.count.times do |mix|
+  if monkeys[mix] =~ /(\d+)/
+    val = $1.to_i
+    nums[monkeys[mix][0...4]] = $1.to_i
+    monkeys[mix] = nil
+  end
+end
+monkeys.compact!
+
+while nums["humn"].nil?
+  monkeys.count.times do |mix|
+    f, a, b = monkeys[mix].scan(/[a-z]{4}/)
+    unless nums[a].nil? || nums[b].nil?
+      case monkeys[mix][11]
+      when ?+
+        nums[f] = nums[a] + nums [b]
+      when ?-
+        nums[f] = nums[a] - nums [b]
+      when ?*
+        nums[f] = nums[a] * nums [b]
+      when ?/
+        nums[f] = nums[a] / nums [b]
+      end
+      monkeys[mix] = nil
+    end
+  end
+  monkeys.compact!
+end
+
+puts nums["humn"]
diff --git a/day21/test b/day21/test
new file mode 100644
index 0000000..e14be60
--- /dev/null
+++ b/day21/test
@@ -0,0 +1,15 @@
+root: pppw + sjmn
+dbpl: 5
+cczh: sllz + lgvd
+zczc: 2
+ptdq: humn - dvpt
+dvpt: 3
+lfqf: 4
+humn: 5
+ljgn: 2
+sjmn: drzm * dbpl
+sllz: 4
+pppw: cczh / lfqf
+lgvd: ljgn * ptdq
+drzm: hmdt - zczc
+hmdt: 32